Bibliographic details of the publications referred to by author in this specification are collected at the end of the description. Sequence Identity Numbers (SEQ ID NOs.) for the nucleotide and amino acid sequences referred to in the specification are defined immediately before the bibliography.
Atherosclerotic coronary heart disease is one of the major causes of death in the western world (World Health Statistics Annual). An earlier event in atherogenesis is the adhesion of monocytes to the endothelium via adhesion molecules such as VCAM-1, ICAM-1 and E-selectin, all of which are rapidly synthesised in response to cytokines. VCAM-1 is primarily involved in the adhesion of mononuclear leukocytes to the endothelium. It is rapidly induced by the inflammatory cytokines IL-1 and TNF-α, and its induction is sustained for 48 to 72 hours. ICAM-1 is expressed on many cells types and is involved in both monocyte and lymphocyte adhesion to activated endothelium. E-selectin is an endothelial specific adhesion molecule important in capturing leukocytes from the axial stream to roll along the endothelium (Abbassi et al., 1993).
There is considerable evidence for the involvement of adhesion molecules in the development of early atherosclerotic lesions and in mature atherosclerotic plaques (Van der Wal et al., 1992). Variable and low levels of E-selectin and VCAM-1 have been detected in the arterial endothelium over plaques (Van der Wal et al., 1992; Wood et al., 1993). VCAM-1 has also been observed in areas of neovascularization and in inflammatory infiltrates at the base of plaques, suggesting that intimal neovascularization may be an important site of inflammatory cell recruitment into advanced coronary lesions (O'Brien et al., 1993). ICAM-1 has been shown to be expressed on the endothelium overlaying atheromatous plaques (Johnson-Tidey et al., 1994).
The signals that lead to upregulation of cellular activities such as expression of adhesion molecules have not been defined. Elucidating these cellular signalling mechanisms is necessary for the development of therapeutic strategies to disease conditions in which said cellular activities are harmful such as coronary heart disease and inflammatory conditions.
In work leading up to the present invention, the inventors have identified a sphingosine kinase signalling pathway via which cellular activities such as adhesion molecule expression are achieved. By regulating the expression and activity of individual components of this pathway, these cellular activities can be modulated. The inventors have also developed a rapid, high volume assay for detecting agents exhibiting sphingosine kinase activity and agents which can act as agonists and antagonists of sphingosine kinase activity.